1. Field of the Invention
The present invention relates to an optical measuring apparatus for accurately measuring a distance to a target object or a group index of an optical path, using optical techniques.
2. Related Background Art
As a conventional rangefinder there is an ultrasonic rangefinder which cannot present high-accuracy results but only can serve as a rough guide. Namely, a problem was that a measuring position could not be finely determined, because there were difficulties in fully converting a beam and specifying a beam-focused position. Another problem was an inability to achieve a satisfactory measurement accuracy, because of the high degree of temperature dependence in the measurement.
As an optical rangefinder there exists an electro-optical rangefinder of a phase-difference method, in which the intensity of signal light is modulated by a sine wave or the like, the signal light is projected onto a target object, a phase of the modulation signal between transmission and reception is measured from a sinusoidal intensity change of reflected light, and a distance is determined based on the phase. Such a rangefinder, however, had a problem that a circuit system therefor became complex and expensive.
As a group index meter there also exists an electro-optical rangefinder of the phase-difference method, in which the intensity of signal light is modulated by a sine wave or the like, the signal light is projected onto a reflector grounded at a known distance, a phase of the modulation signal between transmission and reception is measured from a sinusoidal intensity change of reflected light, and a group index of a substance filling the optical path is determined based on the phase. The rangefinder of this type, however, had a problem that a circuit system therefor became complex and expensive.